Fabric and process of preparing same



Patented Ma 11, 1937 UNITED s'rm'as PATENTIOFFICE FABRIC AND P333123: OF PREPARING Winfield Walter Heckert, Ardentown, Del., as-

signor, by mesne assignments, to E. I. du Pont de Nemours & Company, WllmingtomDeL, a corporation of Delaware No Drawing. Application February 8, 1936, Serial No. 62,993

20 Claims.

This invention relates to improved pile fabrics, and it pertains particularly to the production of pile fabrics comprising a regenerated cellulose pile treated with formaldehyde, said fabrics having a greatly improved resistance to crushing.

There are various forms of pile fabrics comprising rayon pile, e. g., a pile composed of threads of regenerated cellulose rayon made by the viscose process. One form of pile fabric is that popularly known as transparent velvet, in which the ground warp or backing and filler are natural silk threads, and in which the pile warp or pile is regenerated cellulose thread. Transparent velvet and other pile fabrics are made by interweaving the pile warp with two ground fabrics, each of which comprises a ground warp and a ground filler, the two ground fabrics being connected by the pile warp. The composite double woven fabric comprising the two ground fabrics and the pile warp is divided by cutting the pile warp threads intermediate the ground fabrics, thereby dividing the composite woven fabric into two fabrics, each of which comprises a ground warp and filler and a pile.

One of the great disadvantages of transparent velvet as manufactured in the past, resided in the fact that the pile was easily crushed, that is, a slight crushing pressure caused the pile to be permanently crushed toward the ground fabric, thereby imparting to the fabric and to dresses or other apparel made therefrom an unsightly appearance. The inability of such fabrics to resist crushing was particularly noticeable when the fabric was subjected to crushing at high relative 3-3 humidity, e. g., a relative humidity above 60%.

Dresses and other garments made from transparent velvet are subjected, during normal usage, to conditions of high relative humidity.

One object of this invention relates to the production of pile fabrics having improved crush resistance and exhibiting the pleasing softness desired in such fabrics. Another object of the invention pertains to the production of pile fabrics containing a regenerated cellulose pile which 45 is highly crush resistant. A further object of the invention is to prepare transparent velvet having improved resistance to crushing or matting of the pile particularly at high relative humidity, said velvet being of light weight and having an attractive hand or feel. Other objects of the invention will appear hereinaften.

The objects of the invention are accomplished in general by treating a pile fabric having a regenerated cellulose pile with formaldehyde, the ground fabric or backing being substantially nonreactive towards formaldehyde.

In carrying out the invention, pile fabrics such dyed in the usual manner. The velvet is impregnated with a solutionof formaldehyde and an acid or acid salt catalyst and dried at a temperature of 200-250 F. During the drying process the velvet pile is carded, i. e., brushed first in one direction and then in the opposite direction until at the end of the drying process the pile threads stand perpendicular to the backing. Drying may take only 5-10 minutes and may or may not be followed by a period of baking at the same or higher temperatures in order to'complete the reaction. The resulting velvet is found to be resistant to crushing, particularly at high relative humidities.

Example 1 A sample of transparent velvet comprising a silk backing and a viscose rayon pile was dyed and finished in the usual manner. It was stretched upon a stenter frame and an equal weight of an aqueous solution containing 0.5% ammonium chloride and 24% formaldehyde was carefully painted on the backing side of the velvet. The solution was immediately carried to all parts of the vis cose rayon pile by capillary action, but the pile arrangement was left undisturbed. The velvet, still stretched on the frame, was dried in an oven at 200 F. The same result could have been obtained by impregnating the velvet in the formaldehyde solution' subsequent to dyeing, removing all but about an equal weight of solution by suction, and finally drying over heated plates while brushing the pile back and forth. The plates should be heated to such a temperature as to cause the drying to take place at about 200 F.

The product had an attractive hand. It had gained no more than a few per cent in weight and was highly crush resistant. This could be shown by twisting it by hand and comparing with an untreated sample of transparent velvet. The latterwas badly marked by the twisting. A better test was to place a portion of the sample along with the sample of untreated transparent velvet in a desiccator over 5% sulfuric acid (about 98% relative humidity). After 4-5 hours at this relative humidity the velvets were weighted with 500 gram weights covering a circle 1 inches in diameter. (A pressure about equal to that exerted by an average person sitting in a chair.) One hour later the weights were removed and the fabrics were allowed to recover at relative humidity. Under these conditions it was barely possible to discern where the treated sample had been weighted. The untreated velvet was very badly crushed. Tearing strength determinations made as described on page 448 in Haven: "Mechauical Fabrics, indicated that there had been no loss in strength of the formaldehyde treated fabric.

Example 2 A sample of unfinished transparent velvet was impregnated with a. solution containing 12% formaldehyde and 0.5% ammonium chloride. It was then extracted and dried over hot plates while brushing the pile as is the usual commercial practice in finishing transparent velvet. The last plates were heated above 212 F.

In order to remove the formaldehyde odor remaining on the fabric, the latter was passed for one minute through an aqueous bath containing 1% NHz held at about 200 F. and dried while brushing the pile.

The resulting velvet carried not a trace of formaldehyde odor. It was compared with a sample of velvet which had been crush proofed with ureaformaldehyde resin. It had a much softer and more attractive feel since no resin had been used in the treatment. When crushed for 18 hours at 50% relative humidity with a weight of 500 grams on a 1 /2 cap it recovered much better than an untreated velvet and just as well as the urea-formaldehyde treated velvet. When the crushing was carried out for 2 hours at 98% relative humidity it recovered much better than either the urea-formaldehyde treated velvet or the untreated velvet.

Example 3 A sample of finished transparent velvet was treated with a solution of 37% formaldehyde and 0.25% ammonium chloride in a manner similar to that described in Example 1. In order to remove the strong odor of formaldehyde remaining on the fabric it was baked for 30 minutes in a strong current of air at 302 F. Not more than a trace of formaldehyde odor remained. A similar sample was baked 5-10 minutes at 302 F. in an atmosphere of gaseous ammonia. The odor of formaldehyde was completely removed. Both products were exceedingly crush resistant.

Example 4 A sample of transparent velvet was treated with a solution of 8% formaldehyde, 0.5% ammonium chloride and 3% formamide in the manner described in Example 1. The velvet was then baked 10 minutes at 302 F. This removed every trace of formaldehyde odor. A similar sample containing no formamide still bore some formaldehyde odor. At 98% relative humidity these samples were definitely superior in crush resistance to a sample treated with urea formaldehyde resin but at lower relative humidity they were inferior to the urea-formaldehyde treated sample. The use of formamide gave an improvement in the softness of the pile.

Example 5 Example 6 A transparent velvet was impregnated with an aqueous solution containing 8.5% formaldehyde. 3.8% potassium alum and 1.4% lactic acid, fastened to the outside of a centrifuge basket and centrifuged to remove excess liquid and straighten the pile and was then dried at F. It was found to be much more crush resistant than the untreated control, particularly at high relative humidity.

Example 7 An equal weight of a solution made up from 7 parts hexamethylene tetramine, 18.3 parts 38% hydrochloric acid, and 74.7 parts water was painted upon the back of a piece of transparent velvet. and dried at 200 F. It was highly crush resistant but contained considerable ammonium chloride which could have been removed by washing as described in Example 5.

Example 8 A sample of finished transparent velvet com prising a regenerated cellulose pile and a silk backing was passed over a roll which in turn dipped into an aqueous solution containing 40% formaldehyde and 0.6% ammonium chloride. By this means an amount of solution approximately equal to 30% of the weight of the fabric was applied. The velvet was then dried in an oven at about 200 F. It was found to be very crush resistant.

Example 9 An equal weight of a solution of 37% formaldehyde and 0.5% ammonium bromide was applied to the back of a sample of finished transparent velvet comprising a regenerated cellulose pile and a silk backing. The sample was dried at 200 F. It was found to be crush resistant.

Example 10 A sample of transparent velvet was treated with an aqueous solution containing 37% formaldehyde and 0.5% ammonium sulfite in the manner described in Example 9. The product was crush resistant.

Example 11 A preferred procedure and preferred conditions are illustrated as follows:

A transparent velvet is impregnated with an aqueous solution containing l0 15% formaldehyde and 0.2 0.3% ammonium chloride. and is dried at temperatures gradually increasing to 200 240 F. and then held at this temperature for a period of 4-10 minutes. The fabric is then washed with water containing about 1% ammonia and about 0.5% trisodium phosphate, the excess solution being removed without rinsing and the fabric dried While brushing the pile. The dried fabric contained a small amount of trisodium phosphate. If desired, the fabric may be washed with an aqueous solution containing about 1% ammonia and also containing, if desired, about 0.5% trisodium phosphate, the fabric then being rinsed with an aqueous solution containing about 0.5% trisodium phosphate.

Because of availability, and low cost, formaldehyde is the preferred agent. Paraformaldehyde and other substances which yield formaldehyde such as hexamethylene tetramine can be used.

In addition to the catalysts specifically mentioned in the examples for efi'ecting the combination of regenerated cellulose and formaldehyde, namely ammonium chloride, potassium alum, hydrochloric acid, ammonium bromide and ammonium sulfite, numerous other catalysts exhibiting an acid reaction in aqueous solution may be employed, for example, aminosulfonic acid,

aluminum thiocyanate, aluminum chloride, ferric chloride, etc. Y The catalyst chosen in any particular case will be one which is sufllciently powerful to effect the degree of chemical reaction desired between the regenerated cellulose and the formaldehyde. without weakening the pile to such an extent that it will break off on crushing. This is, of course, within the skill of the experimental chemist. Because of its cheapness and effectiveness, ammonium chloride is the catalyst which is preferred in the exercise of the invention.

A very simple measure of the'extent to which the regenerated cellulose has reacted with the formaldehyde is the increase in weight occasioned by the reaction. In order to determine this increase in weight skeins of the same yarn as that used in weaving the pile of the above transparent velvets were dried, weighed and formaldehyde treated under the same conditions as the velvets. They were then boiled, first in water containing 0.025% trisodium phosphate, and then in three successive baths of boiling pure water for a period of 15 minutes. After drying the gain in weight as per cent of the original weight was recorded.

As the concentration of formaldehyde was raised appreciable crush resistance was obtained when the velvet was treated with an aqueous solution containing about 8% formaldehyde and ammonium chloride and dried at 200 F. Skeins treated in a similar manner gained from -22% in weight. velvets treated in this manner are definitely crush resistant at 98% relative humidity but at 50% relative humidity they are little if any better than the untreated transparent velvet control fabric, (the control fabric being relatively good at low relative humidities).

Treatment with an aqueous solution containing 12% formaldehyde and 0.5% ammonium chloride and drying at 200 F. gave excellent crush resistance at 98% relative humidity and relative humidities. was slightlybrittle and severe twisting of the pile.

a moderate improvement in crush resistance at 50% relative humidity. Skeins treated in a similar manner gained about 4.4% in weight.

Treatment with water containing 37% formaldehyde and 0.5% ammonium chloride in the manner described above gave samples with remarkable crush resistance at both high and low The pile in these samples velvet would break loose a small amount of Ordinary handling did not break loose the pile. Skeins treated in this manner gained 9.5 13.5% in weight. It is preferred that the concentration of the ammonium chloride catalyst be maintained somewhat below 0.5%, e. g., 0.2- 0.3% in order to avoid the embrittlement of the pile.

The use of an aqueous solution containing 37% formaldehyde and 0.5% ammonium bromide gave an increase in weight of 15.7%; the use of ammonium iodide an increase in weight of 14.7%, and the use of ammonium sulfite an increase of lib-9.7%. In all of these cases the drying temperature was 200 F. The use of 0.5% ferric chloride and 37% formaldehyde, dried at266 F. gave ari'increase in weight of 17.8%.

With different catalysts in particular there does not seem to be a linear relationship between crush resistance and the increased weight occasioned by formaldehyde treatment. A very simple method for determining the conditions suitable for industrial operation is to at first employ a relatively high concentration of an acid or an acid salt catalyst, say in therange 05-15%, a relatively high concentration of formaldehyde, for example 20.47%, and a drying and baking temperature high enough to give a fabric with a definitely brittle pile as determined by severe twisting. The concentration of catalyst and of formaldehyde, or both, is then lowered in successive experiments until the fabric no longer shows objectionable brittleness. -At this point there is obtained a. fabric which will be found to have crush resistance. All useful products prepared so far have fallen within the range in which the formaldehyde treatment has increased the weight of the pile between 1.5% and 18% and the better ones in the range 448%.

Lactic acid, when used as a catalyst, is preferably used in the presence of an acid salt, e. g, potassium alum. The salts of hydrochloric, hydrobromic and hydroiodic acids with weak bases are the preferred catalysts, e. an, ammonium chloride, ammonium bromide, and ammonium iodide. Other acids and salts are known which will work. Alkaline materials do not catalyze the reaction.

Drying should not be carried out much below 175 F. unless it is followed by a baking period at a higher temperature. Drying temperatures up to about 320 may be employed. 200-250 F. are preferred.

In commercial practice conditions must be chosen which give the desired degree of crush resistance without serious embrittlement of the pile. In general the products become more crush resistant and more brittle the higher the concentration of catalyst and of formaldehyde employed, the higher the temperature of drying or baking, and the more solution remaining on thefabric as it passes into the drier. When drying over a heated plate rather than in an even it is possible to lower the concentration of catalyst and get the same effect because there is an accumulation of formaldehyde and catalyst at the base of the pile as the drying proceeds. When using an aqueous solution of ammonium chloride as a catalyst it is generally necessary to use at least 0.15% catalyst, at least 8% =formaldehyde, apply about an equal weight of solution to the velvet and dry at 200 F. in order to obtain a reasonably crush resistant velvet. For most purposes it is desirable to increase the amount-of ammonium chloride to 0.20-.3% and to increase the concentration of formaldehyde to 10-40%. A moderate degree of brittleness in the pile is not particularly objectionable since transparent velvets are not subjected to much wear.

Any of the usual softening agents may be used along with the formaldehyde solution. In transparent velvet, softness is a highly prized quality. As softening agents may be mentioned sodium dodecyl sulfate, sodium octadecyl sulfate, sulfonatedoils, glycol monoesters, triethanolamine monostearic acid esters, and in particular formamide. In case the velvet is to be washed subsequent to formaldehyde treatment these softening agents are added to the washing bath. Oils may be appliedto the velvet before or during formaldehyde treatment in order to protect the silk backing during baking.

Washing in pure water requires too long to remove the paraformaldehyde deposited in the velvet during the drying step. The use of dilute ammoniawas found to greatly reduce the time of contact necessary for complete removal of 5 the formaldehyde, thereby making a washing step commercially feasible. Concentrations of ammonia greater than 1% can be employed but are wasteful of ammonia. The addition of 0.5% trisodium phosphate to the washing bath was found to give the fabric a cleaner odor. Other washing agents such as aqueous solutions of sodium silicate, sodium carbonate or other salts, particularly alkali metal salts, which react alkaline when dissolved in water, could undoubtedly be used in place of trisodium phosphate. It is desirable to leave a small amount of the alkaline material on the washed and dried velvet in order to stabilize the cellulose formal from decomposition in the presence of moisture and heat.

Baking to remove the residual paraformaldehyde which imparts the objectionable odor to the fabric may be carried out at temperatures below and above 300 F. At lower temperatures longer times are required. At higher temperatures shorter times are required but there is danger of imparting a scorched odor to the velvet. Baking in ammonia gas lowers the tem perature required, or reduces the time required and causes a more complete removal of the para formaldehyde.

Formamide was found to constitute a particu larly good softener for the pile of formaldehyde treated velvets. Furthermore, it seemed to wipe up" traces of paraformaldehyde remaining in the velvet, thereby shortening the time required for baking.

In order to prevent weakening of the velvet it is essential that the backing be essentially unreactive with formaldehyde. Thus it should preferably be made out of silk. Cellulose acetate or wool fibers might also be used in the backing. The term, essentially unreactive with formaldehyde or its equivalent, as used in the specification and claims, signifies a backing composed of 45 thread which is not materially harmed or weakened in the presence of the formaldehyde reagent solution.

While this invention will improve the crush resistance of all types of pile fabrics which have a rayon pile and an unreactive backing, it is of most value in improving the crush resistance of transparent velvets for dress fabrics.

It has thus been found that the practise of the present invention makes it possible to produce pile fabrics having a regenerated cellulose pile which can be dyed and then treated with formaldehyde and produce remarkable, practically unstiifened crush resistant fabrics with good tearing strength and a particularly pleasing hand.

it is possible by the proper choice of dyes to achieve perfectly even dyeing.

When ordinary velvet is submerged in water it comes out with the pile disarranged, having the appearance of a drowned rat. Even steaming will not restore the pile to its original condition. 'Velvets treated with urea-formaldehyde are likewise quite water sensitive although they are an improvement over untreated velvet. A con- 70 siderable proportion of the resin is ordinarily dissolved out by even cold water. Crush resistant velvets properly prepared by the present process are remarkable in that they can be submerged in water and will still dry out to an almost perfect 5 condition. Furthermore, they respond remark- Since dyeing precedes formaldehyde treatment,

ably well to steaming if they have been slightly crushed by wear. In this property they are to be contrasted with velvets made with a. cellulose acetate pile since the latter are relatively crush resistant but once crushed cannot be steamed back into condition.

Crush resistant velvets prepared by treatment with urea-formaldehyde resins liberate formaldehyde in the presence of perspiration, or when warmed with water or water vapor. Formaldehyde odor is very objectionable. velvets prepared by this invention, when properly washed with ammonia solution and stabilized with an alkaline salt, such as trisodium phosphate, do not w liberate formaldehyde under these conditions. This is an important advantage.

It will be understood that although the invention has been described with respect to regenerated cellulose rayon produced by the viscose process, the invention can also be applied to the treatment of pile fabrics containing a pile of regenerated cellulose produced by other processes, for example, the cuprammonium cellulose process.

Parts and proportions given in the above examples and descriptions are intended to be parts by weight, unless otherwise qualified.

Since the invention is susceptible of considerable variations, any departure from the specific examples and description given above which conforms to the spirit of the invention is intended to be included within the scope of the claims.

I claim:

l. A crush resistant pile fabric comprising a pile composed of regenerated cellulose threads having formaldehyde chemically combined therewith and a backing which is substantially non-reactive to formaldehyde.

2. A crush resistant pile fabric comprising a pile composed of regenerated cellulose threads chemically combined with formaldehyde and a backing which is substantially non-reactive to formaldehyde, said pile, due to said chemical combination, weighing from 1.5% to 18% more than the original regenerated cellulose. said fabric, when placed in contact with warm water, being substantially free from formaldehyde liberation.

3. A pile. fabric comprising a pile composed of regenerated cellulose chemically combined with formaldehyde so as to yield a crush resistant pile, said pile containing formamide as a softening agent, said fabric having a backing which is substantially non-reactive to formaldehyde.

4. A pile fabric comprising a pile composed of regenerated cellulose chemically combined with formaldehyde so as .to yield a crush resistant pile, said pile containing a stabilizer for the cellulose-formaldehyde reaction product, said fabric having a backing which is substantially non-reactive to formaldehyde.

5. A pile fabric comprising a pile composed of regenerated cellulose chemically combined with formaldehyde so as to yield a crush resistant 'pile, said pile containing a sufficient amount of an alkali metal salt which reacts alkaline to lit-mus to stabilize the cellulose-formaldehyde reaction product, said fabric having a backing which is substantially non-reactive to formaldehyde.

6. The process of making crush resistant pile fabrics which comprises reacting a regenerated cellulose pile of a pile fabric with formaldehyde, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

'7. The process of making crush resistant pile fir having a backing which is substantially non-' reactive to formaldehyde.

9. The process of making crush resistant pile fabrics which comprises reacting a regenerated cellulose pile of a pile fabric with formaldehyde dissolved in water containing ammonium chloride as a catalyst therefor, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

10. The process of making crush resistant pile fabrics which comprises reacting a regenerated cellulose pile of a pile fabric with formaldehyde dissolved in an aqueous solution containing arnmonium chloride, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

11. The process of making crush resistant pile fabrics which comprises treating a regenerated cellulose pile of a pile fabric with an aqueous solution of formaldehyde containing a small amount of a compound reacting acid in aqueous solution, and heating the pile so treated whereby to effect a condensation of the cellulose and the formaldehyde, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

12. The process of making crush resistant pile fabrics which comprises treating a regenerated cellulose pile of a pile fabric with an aqueous solution of formaldehyde containing a small amount of a compound reacting acid in aqueous-- solution, heating the pile so treated whereby to effect a condensation of they cellulose and the formaldehyde, and then treating the' fabric to remove the odor of formaldehyde, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

13. The process of making crush resistant pile fabrics which comprises treating a regenerated cellulose pile of a pile fabric with an aqueous solution of formaldehyde containing a small amount of a compound reacting acid in aqueous solution, heating the pile so treated whereby to effect a condensation of the cellulose and the formaldehyde, then treating the fabric to remove the odor of formaldehyde and impregnating the fabric with-a stabilizer for the celluloseformaldehyde reaction product, said pile fabric having a backing which is substantially nonreactive to formaldehyde.

14. The process of making crush resistant pile fabrics which comprises treating a regenerated cellulose pile of a pile fabric with an aqueous solution of formaldehyde containing a small amount of a compound reacting acid in aqueous solution, heating the pile so treated whereby to effect a condensation of the cellulose and the formaldehyde. then treating the fabric to remove the odor of formaldehyde and impregnating the fabric with a suflicient amount of a stabilizer to stabilize the cellulose-formaldehyde reaction product which stabilizer comprises an alkali metal salt which reacts alkaline in aqueous solution, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

15. The process of making crush resistant pile fabrics which comprises treating a regenerated cellulose pile of a pile fabric with an aqueous solution of formaldehyde containing a small amount of a compound reacting acid in equeous solution, heating the pile so treated whereby to effect a condensation of the cellulose and the formaldehyde; impregnating the fabric with an aqueous solution containing a sufficient amount of a salt which reacts alkaline in aqueous solution to stabilize the cellulose-formaldehyde product formed, and drying the fabric while retaining at least a portion of said salt in the fabric,

said pile fabric having a backing which is sub- I stantially non-reactive to formaldehyde.

16. The process of making a crush resistant transparent velvet which comprises treating a fabric comprising a regenerated cellulose pile of a pile fabric and a silk backing with an aqueous solution containing -15% formaldehyde and. 0.2-0.3% ammonium chloride, drying the fabric at 200-240 F. for 4 to 10 minutes, washing the fabric with an aqueous solution containing about 1% ammonia and about 0.5% trisodium phosphate, removing excess solution, and drying the fabric, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

17. The process of making crush-resistant pile fabrics which comprises reacting a regenerated cellulose pile of a pile fabric with formaldehyde dissolved in water containing ammonium bromide as a catalyst therefor, said pile fabric having a backing which is substantially non-reactive to formaldehyde. 1

18. The process of making crush-resistant pile fabrics which comprises reacting a regenerated cellulose pile of a pile fabric with formaldehyde dissolved in water containing ammonium iodide as a catalyst therefor, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

19. The process of making crush-resistant pile fabrics which comprises treating a regenerated cellulose pile of a pile fabric with an aqueous solution of formaldehyde containing a small amount of a compound reacting acid inaqueous solution, heating the pile so treated whereby to effect a condensation of the cellulose and the formaldehyde, impregnating the fabric with an aqueous ammoniacal solution containing a sumcient amount of a salt which reacts alkaline in aqueous solutions to stabilize the cellulose-formaldehyde product formed, and drying the fabric while retaining at least a portion of the said salt in the fabric, said pile fabric having a backing which is substantially non-reactive to formaldehyde.

20. A crush resistant pile fabric comprising a pile composed of regenerated cellulose threads chemically combined with formaldehyde and a backing which is substantially nonreactive to formaldehyde, said pile, due to said chemical 

